The present invention relates to a nozzleless ink printer in which surface acoustic waves are utilized to cause ink to be jetted in the form of mist.
In an ink jet printer, ink droplets are jetted to record characters or patterns on the recording sheet according to input data. Thus, the ink jet printer is advantageous in that it is noiseless, and data can be recorded directly on ordinary sheets of paper. However, the ink jet printer is still disadvantages in the following points.
It is necessary to provide a number of ink pressurizing chambers and bubble forming chambers for a small printing head, and to connect a number of nozzles to those chambers with high density. Hence, in the manufacture of the ink jet printer, the molding technique must be considerably high in precision, which obstructs reducing the manufacturing cost. Furthermore, because of the drying of ink or the deposition of dust, the nozzles are liable to be clogged. Thus, the ink jet printer is relatively low in reliability.
In order to overcome the above-described difficulties, recently intensive research has been conducted on an ink ejector utilizing surface acoustic waves.
Japanese Unexamined Published Patent Applications Nos. 10731/1978 and 14881/1981 disclose the first ink ejectors of a type in which surface acoustic waves are utilized to jet or transfer a liquid. However, those devices suffer from the same problems as the ink jet printer because they require nozzles and liquid flow paths.
U.S. Pat. No. 4,697,195 discloses a device in which a number of pairs of comb-shaped electrodes are formed concentrically on the surface of a piezoelectric substrate held immersed in solution, and high frequency voltage is applied to those electrodes to generate surface acoustic waves on the surface of the piezoelectric substrate. Conical leakage vertical oscillations induced by the surface acoustic waves thus produced are concentrated at the solution level to jet solution droplets onto the recording medium. This device is epoch-making in that it uses no nozzles to jet solution droplets. However, in view of its construction, it is considerably difficult to realize the multi-element print which is required for providing the device as an actual printer.
The ink jet system disclosed in the publication "Japan Acoustic Society Lecture Papers", March 1989, by Shoko Shiokawa et al. is based on the phenomenon that, when a liquid droplet is placed on the propagating surface of a surface acoustic wave, the liquid is caused to flow in the direction of propagation by the surface acoustic wave excited therein, and a liquid-mist consisting of liquid particles is jetted from the other side of the liquid droplet. The ink jet system is significant for realizing a nozzleless printer. However, the system is still disadvantageous in that, as was pointed out in the publication, the flow of the liquid is liable to be affected by the condition of the surface of the substrate, and depending on the quantity of the liquid droplet the surface curvature is changed or the propagation path in the liquid is shifted, and therefore it is impossible to correctly control the direction of the ink mist discharged from the liquid droplet's surface.